1. Field of the Invention
The present invention relates generally to devices and methods for optically analyzing biological fluids. In particular, it relates to the design and use of centrifugal rotors which allow precise measurement and delivery of a predetermined volume of a fluid to a chamber in the rotor.
Blood plasma and other biological tests frequently require that liquids be quickly divided into predetermined volumes for analysis in a variety of optical tests or assays. It is also frequently desirable to separate potentially-interfering cellular components of the material from the biological fluid prior to testing. Such measurement and separation steps have heretofore been typically performed by centrifugation to separate, for instance, blood plasma from the cellular components, followed by manual or automated pipetting of predetermined volumes of the blood plasma into separate test wells. Such procedures are labor intensive and time-consuming, and various automated systems and methods have been proposed for providing multiple aliquots of plasma suitable for testing in a more efficient manner.
Of particular interest to the present invention are centrifugal rotors which have been modified both to measure volumes of fluid, such as blood, followed by mixture of the fluid with an appropriate diluent and/or separation of fluid from cellular components. Such rotors can additionally provide a plurality of discrete volumes in separate test wells which may be optically tested or evaluated.
Prior art rotors have frequently utilized complex designs which are difficult and costly to manufacture. Often, the rotors require various separable parts or components which are brought together or separated at different points in the centrifugation procedure. Previous centrifugal rotors have often been limited in the number of discrete samples and test wells which they can provide, and in some cases require the use of a separate displacement fluid to effect flow of blood and plasma through the system.
For these reasons, it would be desirable to provide improved centrifugal rotors and methods suitable for quickly and easily measuring a predetermined volume of fluid, delivering the predetermined volume of fluid into, for example, chambers suitable for separation of cellular components and ultimately distributing the fluid into test wells within the rotors for analysis. Additionally, the rotors should be capable of measuring and distributing relatively small volumes of fluid.
The rotors should be able to accommodate relatively large numbers of test wells or cuvettes, and the rotor design should be simple and amenable to low-cost manufacturing procedures. In particular, it would be desirable if the rotors were of unitary construction with no separable or movable parts. Liquid measurement separation methods should be simple and be capable of being performed in relatively short times. In particular, the methods should require relatively few steps and should be capable of being performed with little or no intervention or manipulations by the operator. It would be particularly desirable if the methods required only rotation of the rotor in order to effect measurement and delivery of the fluid.
2. Description of the Background Art
U.S. Pat. No. 4,894,204 discloses a centrifugal rotor having a calibration vessel connected to an overflow vessel. The calibration vessel has a feed orifice through which it communicates with a central receptacle and an exit orifice located in the wall opposite the feed orifice. The exit orifice is designed such that liquid begins to escape from the calibration vessel from the start of its being filled. U.S. Pat. No. 4,284,602 describes a centrifugal rotor in which measuring chambers are positioned between an inlet and the reaction chamber. An overflow chamber is provided to receive excess fluid. Flow from the measuring chamber, however, is effected by use of a heavier displacement fluid, rather than by an increased rotational speed. U.S. Pat. No. 3,899,296 describes a rotor for performing photometric analyses of whole blood samples in which the cellular component is separated from the plasma and measured subvolumes of the plasma are distributed to sample analysis cuvettes. Delivery of the measured volumes is obtained by applying a slight positive air pressure to the passageways containing the plasma. U.S. Pat. No. 4,469,793 relates to centrifugal rotor having a measurement chamber having inlet and outlet orifices. The outlet orifice leads to passages which carry liquid to an overflow chamber when the rotor is rotating in a first direction and to a receptor cell when the rotor is rotating in a second, opposite direction.
The following patents do not provide for measurement of a predetermined volume of fluid as the rotor spins. U.S. Pat. No. 3,864,089 describes a rotor for blood fractionation. U.S. Pat. No. 4,279,862 is directed to a rotor which has means for creating a pressure differential and/or turbulence to produce a homogeneous mixture of reagent and sample. U.S. Pat. No. 4,509,856 is directed to a rotor useful for photometric analysis of a sample. U.S. Pat. No. 4,515,889 relates to the rotor having a plurality of interconnected small hollow spaces adapted for mixing reaction components. U.S. Pat. No. 4,689,203 relates to a centrifugal rotor designed for separating blood plasma from red and white blood cells.